The present invention relates to a material having a low dielectric constant (low k material) useful as an insulating film used for interlayer insulation of semiconductor elements, as a barrier metal layer or an etch stopper layer, or as a substrate for electric circuit parts, and also relates to an insulating film comprising this material and a semiconductor device having the insulating film.
Demands for high integration and high speed of semiconductor devices are increasing more and more. In order to meet these demands, there have been made a study on conductive layer materials having a lower electric resistance than conventional aluminum alloy, namely a study on wiring materials, and a study on insulating layer materials having a lower dielectric constant than conventional silicon oxide. In particular, these materials are needed in wiring of semiconductor devices if the structural minimum dimension of the semiconductor devices becomes smaller than about 0.18 μm, as known, for example, from “Recent Development in Cu Wiring Technology” edited by S. Shinmiyahara, N. Awaya, K. Ueno and N. Misawa published by Realize Company, Japan in 1998.
FIG. 5 is a section view showing a two layer copper wiring structure in a semiconductor device disclosed in the above publication. In the figure, numeral 1 is a silicon substrate, and numeral 2 is a first insulating layer having trench 3 corresponding to a first wiring pattern. The first insulating layer 2 is made of a silicon oxide film having a dielectric constant of 4.2 or a fluorine-containing silicon oxide film having a dielectric constant of 3.2 to 3.5. Further, studies have been made on applicability, as alternates, of materials having a lower dielectric constant than 2.8 such as silicon-based inorganic polymer materials, organic polymer materials, amorphous fluorine-containing carbon films and porous silicon oxide films. The bottom and the side faces of trench 3 are covered with first conductive film 4 having a diffusion preventive function as a barrier metal. Titanium nitride (TiN), tantalum nitride (TaN), tungsten nitride (WN), or a trinaty barrier metal comprising each of these nitrides and silicon is used as the first conductive film 4. First copper conductive layer 5 is formed to fill the trench 3 covered with the first conductive film 4. Numeral 6 is a first insulating film having a diffusion preventive function against copper, which is made of silicon nitride. Numeral 7 is a second insulating layer, which is made of a material similar to that of the first insulating layer 2. A hole 8 is formed in the first insulating film 6 and the second insulating layer 7 therethrough, and the bottom and side surfaces of the hole 8 are covered with a second conductive film 9 having a diffusion preventive function and contacting the first copper conductive layer 5. The hole 8 which is covered with the second conductive film 9 is filled with a second copper conductive layer 10. A trench 12 corresponding to a second wiring pattern is also formed in the second insulating layer 7, and the inner surfaces of trench 12 are covered with third conductive film 11 having a diffusion preventive function. The trench 12 which is covered with the third conductive film 11 is filled with a third copper conductive layer 13. The second and third conductive films 9 and 11 are made of a material similar to that of the first conductive film 4. The upper surface of the third copper conductive layer 13 is covered with a second insulating film 14 made of silicon nitride having a diffusion preventive function against copper. The first and third copper conductive layers 5 and 13 constitute wiring in the lower layer and wiring in the upper layer respectively, and the second copper conductive layer 10 electrically connects these wirings in the uppcr and lower layers therebetwe en. While the wiring of two layer structure is shown in FIG. 4, this structure may be repeatedly stacked to form a multi-layer structure.
The wiring structure shown in FIG. 5 is formed through a so-called Damascene process, which will be described below.
Trench 3 corresponding to a wiring pattern is formed in first insulating layer 2, and first conductive film 4 which serves as a barrier metal, is formed on the inner surface of the trench 3. A copper film is then formed on the first insulating layer 2 to fill the trench 3. Unnecessary barrier metal and copper films formed on portions other than the trench 3 are removed by CMP (chemical mechanical polishing) to leave the barrier metal and copper only in the trench 3 to form first copper conductive layer 5. In such a manner, the copper wiring in the lower layer is formed in the trench 3 with the bottom and side surfaces thereof covered with the first conductive film 4. Then, silicon nitride film 6 and second insulating layer 7 are sequentially stacked on the first insulating layer 2. Trench 12 having a pattern corresponding to the second wiring and hole 8 extending to the first copper conductive layer 5 are formed in the silicon nitride film 6 and the second insulating layer 7 therethrough. Second and third conductive films 9 and 11 are formed as the barrier metal on the surfaces of the trench 12 and the hole 8. The trench 12 and the hole 8 are then filled with copper by copper film forming, followed by removal of unnecessary copper and barrier metal on the second insulating layer 7 using CMP to thereby form the wiring in the upper layer. Thereafter, second insulating film 14 is formed.
Where a polymeric material or a porous silicon oxide, which have a lower dielectric constant than silicon oxide and fluorine-containing silicon oxide, is used as a material for the first or second insulating layer or the first or second insulating film of semiconductor devices having the above wiring structure, a problem arises about deterioration in reliability of wiring and device. Since these materials have a lower thermal conductivity, as compared with conventionally used silicon oxide, heat generation in the wiring may cause the temperature of semiconductor devices to rise.
FIG. 6 is a section view showing a wiring structure in a semiconductor device disclosed in W. Y. Shih, M. C. Chang, R. H. Havemann and J. Levine, Symposium on VLSI Technology Digest, pages 83-84, 1997, wherein two kinds of insulative materials are used in the above-mentioned first and second insulating layers respectively in order to solve the problem associated with poor thermal conductivity.
A material having a low dielectric constant, such as a polymeric material, is used as a material of insulating layers 15 and 16 in which wiring is formed by each of first copper conductive layer 5 and third copper conductive layer 13. On the other hand, silicon oxide, which has good thermal conductivity and has been conventionally used as an insulating material of a wiring-forming layer, is used as a material of insulating layer 18 in which hole 8 is formed and as a material of insulating layer 17 disposed between first copper wiring 5 and substrate 1, thereby suppressing deterioration in thermal conductivity as a whole. Numerals 4, 9 and 11 denote first, second and third conductive films respectively which are formed as a barrier metal. Numeral 10 is a second copper conductive layer filled in the hole 8. Numeral 12 is a trench, and numeral 14 is a second insulating film.
The former publication describes that because of a scale down of pattern size associated with high integration of integrated circuits in semiconductor devices and an increase in wiring length resulting from an increase in chip area, the propagation delay of signals on wiring is growing to a major cause, hindering the advent of high speed devices. A solution of such a problem would require a reduction in wiring resistance and the use of insulating films having a low dielectric constant for reduction in electrostatic capacitance between wirings, namely reduction in wiring capacitance. As a wiring material for this purpose, copper is beginning to replace conventionally used aluminum alloy. On the other hand, as an interlayer dielectric, for this purpose, a fluorine-containing silicon oxide film, having a dielectric constant of 3.2 to 3.5, namely SiOF, is also beginning to replace silicon oxide, having a dielectric constant of 4.2.
However, in the case of forming an interlayer insulating film from SiOF, its dielectric constant is from about 3.2 to about 3.5 and, therefore, the reduction in capacity between wirings and the prevention of propagation delay of signals on wiring are not sufficiently achieved, although the dielectric constant of interlayer insulating film becomes lower than conventional one.
With respect to interlayer insulating films fanned from organic compounds, a dielectric constant of 2.7 is achieved by a film of a polyimide into which a fluorine atom is introduced or by an aryl ether polymer, but these are still unsatisfactoiy for use as an interlayer dielectric. A deposition film of parylene can achieve a dielectric constant of 2.4, but its thermal resistance is at most about 200-300° C. and, therefore, processes for the production of semiconductor elements are restricted.
Also, a porous SiO2 film having a dielectric constant of 2.0 to 2.5 is reported, but it is poor in mechanical strength (resistance to CMP process) due to high porosity and has a problem that the pore size is not uniform.
Further, these polymeric materials and porous SiO2 film have an inferior thermal conductivity as compared to conventional SiO2 interlayer dielectrics and accordingly may cause a problem of deterioration in wiring life (electromigration) due to rise in temperature of wiring.
Use of copper as a wiring material requires covering the surface of copper wiring with a diffusion preventive film, since copper easily diffuses into insulating layers under application of an electric field. Therefore, in general, the lower and side surfaces of a copper wiring are covered with a conductive barrier metal, while the top surface thereof is covered with a silicon nitride insulating film. The dielectric constant of the silicon nitride film is about 7 and the resistance of the barrier metal is much higher than that of copper. Thus, the resistance value of the wiring as a whole increases to result in restriction on speeding up in operation of semiconductor devices.
The same problem is also encountered when a low dielectric constant material is used as an insulating film. In case of using low dielectric constant insulating films, conventional silicon oxide which has a good thermal conductivity is used as a material of a layer provided with a hole for connecting the upper wiring with the lower wiring in order to avoid reduction in reliability. Since the use of this silicon oxide layer further increases wiring capacitance, a problem arises that the propagation delay of signal is caused by increase in wiring capacitance, thus resulting in restriction on speeding up of semiconductor devices.
As a material having a low dielectric constant and a thermal resistance which would solve the problems as mentioned above, JP-A-2000-340689 and JP-A-2001-15496 propose low dielectric constant materials that have a borazine skeleton-based molecule in an inorganic or organic material molecule. However, the proposed low dielectric constant materials have the problem that since they are hydrolyzable, the water resistance is poor.
It is an object of the present invention to provide a low dielectric constant material free from the problems as mentioned above, particularly a low dielectric constant material having an excellent water resistance as well as a low dielectric constant and a high thermal resistance.
A further object of the present invention is to provide a low dielectric constant insulating film having an excellent water resistance suitable for use in semiconductor devices.
A still further object of the present invention is to provide a process for preparing a low dielectric constant material having an excellent water resistance as well as a low dielectric constant and a high thermal resistance.
Another object of the present invention is to provide a semiconductor device capable of operating in high speed and having a high reliability.
These and other objects of the present invention will become apparent from the description hereinafter.